The present disclosure relates to an image reading device for reading an image from a document sheet by the flat bed method, and an image forming apparatus including the image reading device.
There is known an image reading device which includes an image reading portion for reading an image from a document sheet by the flat bed method. The image reading portion includes a reading unit which includes a reading optical system composed of a light source, a mirror and the like for reading an image from a document sheet. The image reading portion reads the image of the document sheet as an electric signal by causing the reading unit to move in a sub scanning direction to scan the reading surface of the document sheet.
As a drive mechanism for moving such a reading unit in the sub scanning direction, there is known a drive mechanism which is based on the belt drive method. The drive mechanism of this type includes a pair of pulleys, a drive belt, and a drive motor. The pair of pulleys are disposed at positions that are separated by a predetermined distance in the sub scanning direction. The drive belt has an endless shape and is extended in suspension between the pair of pulleys. The drive motor rotationally drives one of the pair of pulleys. The reading unit is attached to the drive belt. When the one of the pair of pulleys is rotationally driven by the drive motor, the drive belt runs in the sub scanning direction. This allows the reading unit attached to the drive belt to run in the sub scanning direction.